You want attack chickens? You got 'em!
This is a simple patch that makes all animals fully trainable (haul, attack, etc) by adding trainability to all animals and removing the size requirement to certain kinds of training (e.g. Hauling).
As well, it removes the need to contain certain animals in pens that was introduced in v1.3 of Rimworld. If you wish to "pen" them, just contain them with Allowed zones like ya did pre-1.3.